Recent developments of the 3GPP Long Term Evolution (LTE) facilitate accessing local IP based services in the home, office, public hot spot or even outdoor environments. One of the important use cases for the local IP access and local connectivity involves the direct communication between devices in the close proximity (typically less than a few 10s of meters, but sometimes up to a few hundred of meters) of each other, an exemplary scenario of which is shown in FIG. 1. As illustrated in FIG. 1, in addition to communications with the BS, two D2D enabled user equipments (UEs) 1 and 2 are also engaging in direct communication with one another. Because D2D enabled UEs are much closer to one another than cellular devices that have to communicate via a cellular access point (e.g., BS or eNB), such a direct mode (or called D2D mode) enables a number of potential gains over the traditional cellular techniques as follows:
capacity gain: First, radio resources (e.g., orthogonal frequency division multiplexing (OFDM) resource blocks) between the D2D and cellular layers may be reused (reuse gain). Second, a D2D link uses a single hop between the transmitter and receiver points as opposed to a 2-hop link via a cellular access point (hop gain).
peak rate gain: Due to the proximity and potentially favorable propagation conditions, high peak rates could be achieved (proximity gain);
latency gain: When the UEs communicate over a direct link or, in other words, in a D2D mode, eNB forwarding is short cut and the end-to-end latency may be decreased.
From the perspective of network coverage availability, D2D communication may be divided into two scenarios, i.e., a network assisted (NWA) case and a non-NW assisted (nNWA) case. In the NWA case, it is possible that the scheduling of D2D communication is controlled by the network, which implements contention-free access schemes. However, the disadvantages in this case are obvious, e.g., it needs a large number of feedbacks about the radio link quality from the D2D enabled UEs to the network, which will cause signaling overhead in the system, especially considering the possible large number of devices in the future system. In the nNWA case, D2D enabled UE transmitters may get the radio link quality information locally, based upon which it may also decide the resource usage details autonomously. These resource usage details include all possible radio resource management (RRM) related aspects, e.g., a modulating and coding scheme (MCS), physical resource block (PRB) positions, power control and etc. In this way, the signaling overhead may be reduced and it relaxes the burden of the central scheduler. However, all these may only be realized under contention-based access schemes. Therefore, how to efficiently convey control/scheduling information from a D2D enabled UE transmitter (i.e., transmitting party) to a D2D enabled UE receiver (i.e., receiving party) without considering the access schemes needs to be addressed.
In the framework of “Flashlinq: A Synchronous Distributed Scheduler for Peer-to-Peer Ad Hoc Networks” as proposed by Xinzhou W U et al., a distributed RRM scheme for D2D communication is proposed. However, this scheme mainly solves the problem of link scheduling, i.e., which D2D link is allowed to access, and does not mention any details in regards to conveying the control information, which would relate to the instant decision of a PRB selection, an MCS, HARQ setting, and etc, from the D2D enabled UE transmitter to the D2D enabled UE receiver. Furthermore, the co-existence problem between D2D channels and cellular channels, as discussed below, is out of the scope in Flashlinq's design.
According to the current discussion status in the 3GPP on the D2D communication, it is widely agreed that the D2D communication may reuse the cellular uplink (UL) resources, including both UL bands for frequency division duplex (FDD) and UL subframes for time division duplex (TDD). This means that the D2D control or data channels and cellular data or control channels (e.g., physical uplink shared channel (PUSCH), physical uplink control channel (PUCCH)) may coexist in the same bands/subframes. It makes the design of the D2D control channel more complicated, i.e., an efficient interference coordination scheme should be taken into account. Therefore, how to determine/map the control channel resource for each D2D link and how the control channel configurations may be known by both D2D enabled UE transmitter and receiver are key factors in designing the D2D control channel.